Oil Ring question

[Michael Beattie]

I have just pulled the pistons out of my HF1600 engine, and I noted a difference in the oil scraper rings with these and another set of pistons I have. One set of pistons has the oil ring with a coil spring behind it. The other set has the oil ring with no coil spring,

Does anyone know if there were differences like these, or are my spare set of pistons missing the oil ring coil springs ? They are the opposite in profile to the set in the engine, having the larger gap in the sideways H to the outside. The ones with the spring have the larger gap on the inside to accomodate the coil.

Cheers

Michael

[william vd Sman]

The rings with the coil are of a newer design than the springless type. Nonetheless completely outdated. modern cars use three segment oilscraper rings consisting of two thoothed flattish rings sandwiching a coil spring. This type (which is allready used for the last 15 to 20 years) had the advantage of less springpressure against the bore while retaining equal or better oilscraping capabilities. When rebuilding my 1200HF my machineshop advised me to trow away the scrapers which came with my NOS Asso forged pistons ans replace them with the current type. Can't tell anything on bore wear yet but oil consumption is allmost nil while the car is used for not much more than trackdays.

[P. de R. Leclercq]

The cast iron ring with the spring expander is the best type - as used on Integrales and Evos etc. The three piece type made of spring steel are horrible and make a very tight engine - I did a jaguar XK engine last year with these rings and it was too much for the starter moter...

At Evolution Engineering we used to throw away the Perfect Circle oil rings for this reason

Paul

[Huib]

Don't confuse pressure and force. The spring action either from the one piece ring or any variety of multi piece oil control ring is a force.
The pressure is that force divided by the surface area of the edges pressing against the bore.

For low oil consumption (although never a goal by itself) I have best results with oil control rings with very small edges. Doesnot matter if the thing is single piece, two piece springloaded or the latest 3 piece Goetze rings. The latter happen to have very small edges which I think is the true reason for their effectiveness in reducing oil consumption. I am not in the piston ring business but I suspect that the complicated construction is to reduce cost of materials. Good quality single piece oil control rings with very narrow edges cost more.

I am rather simple mind and thus think that it does not really matter where the spring force comes from. Either from the ring material itself or any form of springloading or little dwarfs living in the groove who push againts the ring. As long as the edge is very thin there is high pressure while the force can be small

For similar reasons I prefer narrow tires such as the 145R14 on S1 coupes which cut through water, snow and ice much better than wide tires. Or small brake pads like the Dunlop pads which cut through a water layer or dust much quicker than the larger S2 pads.

[P. de R. Leclercq]

Well, of course we did not study rings exhaustively, but we would never willingly use those 3-piece spring-steel rings.

On a decent 2-litre twin cam engine build, we would aim for a short engine turning torque of 10 - 12 lbs ft probably about 15 - 18 newton metres. It is not possible to achieve this with those horrid rings.

Fulvias are a bit more difficult because there is usually a tight spot or better say "stiction"on the crank shaft which makes measurement difficult. This is not always the case though. The best one I ever did was a Fanalone; in this the (replacement - S2) crank spun beautifully.

Paul

Paul

[P. de R. Leclercq]

I would add that also at Evolution we did supply a few sets of beautiful forged pistons from CPS in Italy.

These had 1mm top rings, 1.5mm second rings and the 3mm oil ring was of cast iron with a spring expander.

These were fragile and broke very easily using the usual method on a Fulvia of feeding in the rings. I made a special compressor which solved the problem, after the suppliers kindly sent some replacements.

The engine turned out beautifully I have to say.

Paul

[william vd Sman]

all good and well but why do all today manufacturers use the three piece rings? cannot be for the wish for a tight engine as todays engines run very light. The secret in getting the correct resistance must be the correct size of the rings. Paul, according to you my 80 hp 1200 is a good specimen. This is with three piece rings...

[P. de R. Leclercq]

Well William, in my experience you are fortunate. When trying the spring steel rings I have always been very careful about gapping them correctly to no avail. Sometimes the makers say that they are pre-gapped, but I don' believe them. If it were only me I would question myself, but as I wrote earlier, others have had the same problems.

Apart from numerous Fulvias, I have experienced the same trouble with Jaguars and even with a Delahaye engine that I rebuilt.

Paul